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In this paper, selective formation of noncentrosymmetric (Cc; α-crystal) and centrosymmetric (P21/c; β-crystal) 1,1,2,2-tetramethyl-1-(4-(N,N-dimethylamino)phenyl)-2-(2′-cyanophenyl)disilane (1) wa...

Hydrogenation of nonequilibrium alloys may form nanometer-sized metal hydride clusters, depending on the alloy compositions and hydrogenation conditions. Here in the Ti-rich compositions of the immiscible Mg-Ti system MgH2 clusters are embedded in a Ti-H matrix. Our previous works have indicated that the interface energy between the two metal hydrides reduces the stability of MgH2. The aim of our study is to obtain the structural information on the nanometer-sized clusters. Indeed, MgD2 clusters embedded in a face-centered-cubic (FCC) Ti-D matrix is found in Mg0.25Ti0.75D1.65 by means of 2H magic angle spinning nuclear magnetic resonance (MAS NMR). The atomic pair distribution function (PDF) analysis of neutron total scattering data suggests that the MgD2 clusters have an orthorhombic structure, which is different from a rutile-type body-centered-tetragonal (BCT) structure of α-MgD2 observed in the Mg-rich compositions. Our results suggest that we can tune the thermodynamics of hydrogen absorption and des...

Inorganic solid acid salts with hydrogen bond networks frequently show very long spin-lattice relaxation times even for 1H because the hydrogen bonds suppress motions. In the present work, the 1H spin-lattice relaxation in Cs2(HSO4)(H2PO4) containing a small amount of ammonium ions were studied in detail by use of the effect of magic angle spinning (MAS) on the relaxation. The 1H spin-lattice relaxation times of the acid protons decrease with increase in the content of ammonium ions. Reorientation of the NH4 group fluctuates the dipole-dipole interaction and relaxes the ammonium protons as well as the acid protons. The 1H relaxation times of the acid protons are a little bit longer than those of the ammonium protons at the MAS rate of 8 kHz. The spinning at 50 kHz makes the relaxation times of the acid protons longer and those of the ammonium protons shorter. Spin diffusion between the acid and the ammonium protons averages partially the 1H relaxation of the acid and the ammonium protons at the MAS rate of 8 kHz. The spin diffusion is suppressed completely at the MAS rate of 50 kHz. Spin diffusion between the acid protons is not suppressed at the MAS rate of 50 kHz. The acid protons always show the same relaxation times. The intrinsic relaxation times not affected by spin diffusion are evaluated quantitatively for both the acid and the ammonium protons. Those values are independent of the ammonium content. Contribution of the spin diffusion between the acid and the ammonium protons to the relaxation is estimated quantitatively. Using those parameters, the effect of ammonium ions on the 1H spin-lattice relaxation can be predicted. The 1H spin-lattice relaxation is a sensitive tool to study the distribution of ammonium ions in solids.

Inorganic solid acid salt Cs 2 (HSO 4 )(H 2 PO 4 ) showed high proton conductivity in the superprotonic phase, and the phase was retained on cooling even at room temperature for a long period. In the present work, we attempt partial replacement of Cs ions by ammonium ions. Incorporation of ammonium ions up to 2.3% of the total cations is succeeded. Successful incorporation of ammonium ions is confirmed by the crystal structure measured by X-ray powder diffraction, the phase transition measured by thermal analyses and phosphorus environments measured by 31 P magic-angle-spinning (MAS) NMR. Furthermore, we present 1 H and 133 Cs MAS NMR spectra and the result of 1 H{ 31 P} rotational-echo double resonance (REDOR) experiments. The 1 H and 133 Cs MAS NMR spectra show that incorporation of ammonium ions leads to increase of disordered structures.

This work explores the use of hexagonal boron nitride (h-BN), a graphite-like compound, as a novel catalyst with base and acid functionalities. For use as a solid catalyst, the layered structure of h-BN was disrupted by ball-milling, exposing boron and nitrogen edge sites as well as increasing the surface area from 3 to ca. 400 m 2 g −1 . Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and proton magic-angle spinning nuclear magnetic resonance spectroscopy ( 1 H MAS NMR) indicated simultaneous and adjacent formation of amino and hydroxyl groups by milling, which function as Bronsted base and acid sites, respectively. Analysis using color indicator reagents and pyrrole-adsorbed 1 H MAS NMR results revealed that the ball-milled h-BN had basic sites of strength +9.3 > H − ≥ +7.2, comparable to those of KY zeolite. Measurements of 31 P MAS NMR of adsorbed trimethylphosphine oxide indicated that the ball-milled h-BN had weak acid sites, comparable to those in HY zeolite. Despite its weak basicity, the ball-milled h-BN showed high activity and selectivity toward β-nitroalkenes for the nitroaldol reaction (Henry reaction) and the Knoevenagel condensation, whereas nontreated h-BN did not show activity. The nitroaldol reaction was considered to proceed in two steps: the abstraction of a proton from nitromethane by the amino group and the formation of an imine followed by a nucleophilic attack of the deprotonated nitromethane. Kinetic isotope effect experiments using D -substituted nitromethane revealed that the first step was the rate-determining step. Several nitroaldol reactions using a variety of monosubstituted benzaldehydes indicated that electron-donating groups enhanced the activity, suggesting that the formation of adjacent base and acid sites is responsible for it. This study shows the high catalytic activity of BN, a solid catalyst with moderate basicity and weak acidity.

Mechanisms of the 1 H spin-lattice relaxation in NH 4 H 2 PO 4 were studied in detail by use of the effect of magic angle spinning on the relaxation. The acid and the ammonium protons have different relaxation times at the spinning rates higher than 10 kHz due to suppression of spin diffusion between the two kinds of protons. The intrinsic relaxation times not affected by the spin diffusion and the spin-diffusion assisted relaxation times were evaluated separately, taking into consideration temperature dependence. Both mechanisms contribute to the 1 H relaxation of the acid protons comparatively. The spin-diffusion assisted relaxation mechanism was suppressed to the level lower than the experimental errors at the spinning rate of 30 kHz.

The inorganic solid acid salt Cs2(HSO4)(H2PO4) showed high proton conductivity in the superprotonic phase above 370 K, and the phase was retained on cooling even at room temperature for a long period. These characteristic properties should correlate to the hydrogen bond network connecting the SO4 and PO4 groups. In the present work, the structures of the hydrogen bond network were studied by solid-state NMR. We present 31P, 1H, and 133Cs magic-angle-spinning (MAS) NMR spectra, 31P static NMR spectra to derive chemical shift anisotropy, a 31P{1H} dipolar dephasing experiment, and 1H{31P} rotational-echo double resonance (REDOR) experiments. The 31P NMR spectra indicate that all the P sites are crystallographically equivalent, and the negative value of the chemical shift anisotropy suggests that four hydrogen bonds are formed around the PO4 tetrahedron. The 31P{1H} dipolar dephasing experiment strongly supports that the number of hydrogen bonds around the PO4 tetrahedron is four. The 1H and 133Cs MAS NMR sp...

The interfacing carbon materials can improve the visible light absorption of titanium dioxide (TiO2). Here TiO2 was anchored on carbon spheres (CSs) obtained by the hydrothermal polymerization of sucrose to bathochromically expand its light-response region. Nano-TiO2 is condensed on the CS surface upon hydrothermal treatment to generate a core–shell structure (TiO2@CS). Because of interface formation between the two materials, TiO2@CS achieved an enhanced visible light absorption compared to pure TiO2. In addition, it degraded organic pollutants, such as methyl orange, bisphenol A, and Oseltamivir, more efficiently than pure TiO2 and the well-known graphene–P25 TiO2 nanocomposite under visible light irradiation. This promoted visible light photoactivity was evidenced by the enhanced photocurrent responses and structure-dependent changes of electron spin resonance spectra that disclosed the critical role of an interfacial structure containing a doping level formed by tuning electrons from CS to TiO2. Therefore, the facile hydrothermal formation of TiO2@CS reveals new avenues for cost-effective ultraviolet-free photocatalysts exhibiting high efficiency.

High hydrogen density and low material costs make Mg as one of the most promising candidates for solid-state hydrogen storage. However, the practical applications of Mg are restricted by high reaction temperature and slow kinetics of hydrogen absorption/desorption. Here we present the improvements of both thermodynamics and kinetics of the hydride/deuteride of Mg (MgH2/MgD2) by utilizing the immiscible Mg–Cr system. Nanometer-sized MgD2 domains with the average crystallite size of ~10 nm embedded in a Cr matrix are formed in deuterated Mg0.25Cr0.75. X-ray diffraction and nuclear magnetic resonance spectroscopy studies show that the MgD2 domains are heavily distorted, which leads to the thermodynamic destabilization lowering the reaction temperature. Mg0.25Cr0.75 can reversibly absorb and desorb hydrogen/deuterium at a low temperature of 473 K. The enthalpy ΔH for deuterium desorption of Mg0.25Cr0.75−D is 72.1 kJ mol−1−D2, which is lower than ~74 kJ mol−1−D2 for bulk MgD2. The apparent activation energy for hydrogen desorption of Mg0.25Cr0.75−H is decreased to 75 kJ mol−1 from ~160 kJ mol−1 for bulk Mg, in which the dehydrogenation of nanometer-sized MgH2 is controlled by one-dimensional diffusion of hydrogen. Our work demonstrates that MgH2 nanostructured by an immiscible matrix is a useful strategy to alter the thermodynamic and kinetic properties.

Through various in situ analyses, we have revealed the structural changes that occur during the reversible melting-solidification process of layered alkylsiloxanes (CnLSiloxanes) with carbon numbers (n) of 18 and 16. In situ high-resolution solid-state (13)C nuclear magnetic resonance (NMR) analysis at controlled temperatures indicates drastic conformational changes of the long alkyl chains during the melting-solidification process. A (13)C NMR signal at 33 ppm, which shows the highest intensity at room temperature (RT), is assigned to an inner methylene group with an all-trans conformation. As the temperature increases, the 33-ppm signal intensity decreases while the signal intensity at 30.5 ppm simultaneously increases. The 30.5 ppm signal is assigned to an inner methylene group with a trans-gauche conformation. Subsequently, upon cooling, the signal at 33 ppm recovers, even after CnLSiloxanes have melted. In situ X-ray diffraction measurements at controlled temperatures reveal that the ordered arrangement of the long alkyl chains becomes disordered with elevating temperatures and reordered upon cooling to RT. In situ high-resolution solid-state (29)Si NMR analysis shows that the melting-solidification process progresses without any structural change in siloxane sheets of the CnLSiloxanes. Thus, the in situ analyses show that disordering of the long alkyl chains causes the CnLSiloxanes to melt. Because the majority of long alkyl chains are packed again in the ordered arrangement with the all-trans conformation upon cooling, the CnLSiloxanes are reversibly solidified and the CnLSiloxane structure is recovered.